problem with mid position valve?

[nealegray]

I hope someone can clarify if I have diagnosed the fault that I think Ive got.

A few days ago the central heating started to operate in a strange way. The only way to get the pump to turn on was to have the hot water turned on at the timer. And have the cylinder stat calling for heat.

I believe the problem that I have is that the mid position valve is not working properly and is not energising the orange wire as it should. To test this I have removed the valve wires from the house circuit and done the following to see how the valve reacts.

Blue connected to neutral, earth to earth then I energised white and grey as follows and monitored the voltage on the orange wire and noted the position of the valve.

White_Grey___Orange__Position
__X____X_______X_______W
__/____X___see below___M
__/____/___see below___M
__X____/_______X_______W

X=not energised
/=energised
W= Port B (hot water
M= Port A&B (mid position/both)
H= Port A (central heating)
ignore the lines (_) they are just to space out the table


The voltage on the orange wire was 240v as the valve moved to position M but then it fell to around 82v. And the valve never made it to the H position (ie the central heating position) even though I think it should when the grey and white wires are both energised?

My wiring is (I'm fairly certain) as shown on page5 of the following pdf,

http://www.screwfix.com/sfd/i/cat/pdf/20/p4734620.pdf

the valve is a acl-drayton 679H340-30LO

Any help or advice appreciated.

Cheers
Neale

 

[Slugbabydotcom]

On CH only White goes live.
When valve reaches correct position orange should go live and for some reason its doesnt.
Time 4 a replacement

 

[nealegray]

thats what I figured thanks for the clarification.

 

[seco services]

remove the actuator head from the valve and try it.
try turning the spindle on the valve see if its free, it may be get stiff and the motor can't operate it to the heating position.

 

[OilLecky]

You are correct. The white is "call for heating" and the grey is "hot water satisfied" so with both energised the valve should go to full heating. At the mid-position the 82 volts is to hold the motor in the valve at the half way point. (If there was no supply at this mid-position then the valve would go back to hot water only by return spring pressure). As someone has said, remove the actuator head from the valve and see if the actuator works correctly when off load. Then gently try turning the valve stem to see if it's stuck. (It doesn't move far.)

 

[nealegray]

Ive sorted it.... for now at least, heres what I did.

I replaced the valve motor with one from screw fix, (the valve moved freely), and had the exact same problem. So I took the circuit board out to see if anything had burned out and discovered that both micro switches where faulty. Either giving odd resistances or no continuity at all.

I removed them from the circuit board and carefully prised them apart to see inside. They both had very dirty contacts and one of them had a bent contact causing it to arc when energised. I cleaned them both up resoldered them to the circuit board plugged it all back together and its all working again.

Does anyone know where, (if I need to), I could get replacement microswitches? the ones from maplin dont look exactly right and they are only 3amp, the ones in the valve are 5amp. I'm hoping my repair will be ok but they may fail again.

Thanks for the advice guys.

For anyone with an acl-drayton 679H340-30LO valve, ie the old type without the removable actuator, it IS possible to completely disassemble it as follows;

TURN OFF ALL POWER TO THE CENTRAL HEATING IF YOUR NOT SURE HOW TO DO THIS YOU SHOULD NOT READ ANY FURTHER. CONTINUE AT YOUR OWN RISK.

1. Undo the screw and take off the cover.

2. to remove the motor there are two screws, ones probably hiding behind the orange wires. remove the screws and pull the motor away from the body with the earth plate and heatsink/cover then carefully unplug the connectors from the circuit board. If you need to replace the motor just plug and screw in your new one.

3. to remove the circuit board, slide off the white cover, and undo the two small screws that go through the micro switches. You can now remove the circuit board. (If you havent already you'll also need to remove the cable clip).

4. if you want to go any further, (I didnt), you can remove the actuator bits and springs and there are two screws to remove the actuator body from the valve body. And thats pretty much it.

 

[Slugbabydotcom]

We dont usually faff on with the microswitches because
1 They are generally too fiddly
2 It could be the cogs
3 By the time the microswitches have gone the motor is more than halfway through its life and could well go wrong before the dust settles

Good on ya for figuring it out though and best of luck with it.

 

[OilLecky]

Well nealegray I'm really impressed. I have had many dealings with micro-switches of all sorts in the past. I've opened them to see what has actually happened more than once but I have never repaired one!!!
Go to the top of the "I can fix anything" list!
Now the chances are that the repaired switches will not last long. (sorry!)
Despite much advice not to, I have repaired a Drayton MA1 which has 1 off SAIA, XCG9 and 1 off Burgess, FK4T8 micro-switch fitted. You unfortunately need to establish the actual part numbers of the switches in your unit. Then contact Access Electrical (Services) Ltd.
http://www.access-electrical.co.uk/productsswitches.php
They are very helpful and don't mind dealing with small orders.

The SAIA one is standard and costs about £1 but the Burgess one is another matter and costs nearly £6. (plus postage and package). Still cheaper than a new actuator though!!!
I bought a bag of each and being as I have spent many years repairing actuators of one type or another it doesn't bother me to solder in new switches to actuators and then knock them out at half price. Good luck.

 

[nealegray]

Ooohh top of the class get me.

I kinda figured that the microswitches may not last too long but theyve been ok for 2 days so far so we'll see how they do I guess. Thanks for the link to access electrical. I know one of the switches was definitely a Burgess one but stupidly I did write down any part numbers. At least if they do die again I now know where to get them from.

In hindsight I think that the valve may have died last year, there where times when the house just didnt heat up as quickly or as consistently as you'd expect. We've only been in this house for a couple of years and having previously had night storage heating anything that had even a small amount of control seemed like a bonus. The difference now is considerable.

Thanks again for the helpful responses guys.

Neale

 

[OilLecky]

Neale,

If I were you I'd take the actuator top off again, get the part numbers and order the switches up. You don't want to have Xmas day in the freezing cold being nagged about why you didn't do so and so!!!!!! Anything for peace and quite? Good Luck!